Photographic recording and reproduction of sound



March 30, 1937. M. c. BATSEL :a1-.AL 2,075,496

PHOTOGRAPHIC RECORDING AND REPRODUCTION 0F SOUND Filed Jan. 14, 193s INVENTOR M14/Y 64376? .f5/47562 """mlllll'" U IIINIIIIIIIIIIIIII |||l'"| IIIIIIIIIIIIIIIIIIIIllun"umm"|||IlIlINIIHIlllllllnmglmlh Il HII vnulllll" Patented Mar. 30, 1937 UNITED STATES PATENT oFFicE PHoToGRAPHIc RECORDING AND EEPRO- DUo'rIoN oF soUND Ware Application January 14, 1933, Serial No. 651,738

3 Claims. (Cl. 179-'100.3)

This invention relates to the photographic recording and reproduction of sound, and has for its principal object the provision of an improved photophoncgraphic apparatus and method of op- 5 eration whereby important simplifications in construction and reductions in cost are effected.

As disclosed by United States Patent No. 1,855,197 of Hugh McDowell, Jr., it is customary to provide a photographic sound recorder with lO means for eliminating ground or backgroundv noise due to lm grain, scratches, dust and the like on the normally clear part of the sound track. Various means of accomplishing this result are known. In some of them, a shutter controlled by a rectied component of the recorded audio impulses is utilized to shade the recording light from the normally clear portion of the sound track to an extent dependent on the volume of the recorded sound. In others, a rectified component of the recorded audio impulses is supplied to the recording galvanometer or light valve together with the audio impulses thus shifting the mean position of the galvanometer or biasing the light valve in accordance with the envelope of the sound record and maintaining at a minimum the clear portion of the sound track.

Many or all of these Various recording systems, however, have the disadvantage that an amplifier and rectifier are required to amplify and rectify the current through which the shading effects described above are effected.

In accordance with the present invention this disadvantage is obviated by the provision of an improved apparatus wherein amplification of the recorded impulses and rectification of the ground noise eliminator control current are effected by a single device or element.

The invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended claims:

Referring to the drawing:-

Fig. l is a diagrammatic representation of a sound recording system constructed in accordance with the invention,

Fig. 2 illustrates certain details of a shutter control device of Fig. l,

Figs. 3 and 4 illustrate different types of shutter which may be utilized in the recording apparatus of Fig. l, and

Fig. 5 illustrates a section of sound track produced by the recording apparatus of Fig. l.

This recording apparatus includes a sound pickup or microphone I0 from which the audio impulses to be recorded are supplied through a microphone amplifier a mixer I2, a voltage amplifier I3, an amplifier or driver stage I 4, an out-put .stage amplifier .I5-I5 which is substantially biased tocut-oif, an .output transformer I6, and .afilter |`fI|8|9 to a coil for operating a vibratab'le'mirror 2|) which forms a part of a re-4 cording galvanometer.

The vtype .of amplifier used is ordinarily referred to .asa class B .amplien Such an amplifier is described .on page .296 of Radio Engineering Handbook iby Henney, published by McGraw- Hill Book Company, New York in 1933 and is described in greater detail on pages .16 and 17 of the RCA Cunningham Radiotron'Manual Technical :Series R042, published in 1934 bythe RCA Radiotron Company, Harrison, New Jersey. In this type of amplifier little or no D. C. plate current is drawn by the tubes at Zero modulation, the plate current increasing as the modulation increases, thus distinguishing from the more usual class A amplifier wherein the D. C. plate current drawn remains constant from zero modulation up to a high value thereof.

From the common lead in the output circuit of the amplifier |5-I5, rectified current is supplied through the filter |I-I8-I9 to the operating coils 2| (see Fig. 2) of a ground noise eliminator shutter 22.

Light from a source 23 is applied to the vibratable mirror 20 through a lens 24, a light stop 25 and a lens 26. The light refiected from the mirror 20, past the edge of the shutter 22 and through the lenses 28 and 29, the light slit member 30 and the objective lenses 3| is applied to a light sensitive record such as a motion picture film 21.

Since the push-pull amplifier |5-I5 is biased to cut-off the current supplied to the operating coils 2| of the ground noise eliminator shutter 22 is unidirectional and varies in accordance with the intensity or volume of the audio impulses to be recorded. By suitable design of the filter I1I8| 9 and suitable adjustment of the shunt resistor I9, the rectified current is smoothed out and may be adjusted to the values required to cause the shutter 20 to follow the envelope of the sound record 32 (see Fig. 5), the shading effect being indicated at 33.

The ground noise eliminator device illustrated in Figs. l and 5 is more fully disclosed in a copending application of Edward W. Kellogg, Serial No. 340,087, filed May 26, 1931, for Magnetic shutter motor. How this device and the filter I'I--I8-I9 may be adjusted to cause the shutter 22 to follow the envelope of the sound record will be readily understood by those skilled in the art.

especially in View of the foregoing iplanation. As shown more clearly in Fig. 5, the device includes a magnetic structure 34 provided with bifurcated pole pieces arranged to cooperate with the coils 2|. It also includes a supporting mem ber 35 to which is attached the resilient support 36 of an armature 31 through which the shutter 2l is operated.

'Ihe shutter 2| may assume various forms. As indicated by Fig. 3, it may be V-shaped and so arranged that the divergent edges of the V cut into the light beam in the same manner as the lower edge of the shutter 22 (Fig. 1). The advantage of this type of shutter is that it encounters a different air resistance when moving in opposite directions. Thus, when the bottom of the vane moves in the direction of the bottom of the V it encounters less resistance than when moving in the opposite direction. This shutter, therefore, functions to produce an automatic timing of the'shutter by mechanical means and results in the shutter moving out of the light beam at a relatively high speed and moving into the light beam at a relatively low speed. This shutter may also be in the form of a rotatable disk 38 (Fig. 4) which is operated by a meter mechanism 39-43, the control current being supplied to the operating coil 40 of this mechanism.

Other modifications of the various parts of the apparatus will be apparent to those skilled in the art in vietv of the foregoing explanation.

We claim:

1. Sound recording apparatus including, a push-pull amplifier biased to cut-oi, light control means connected to the output circuit of said amplifier for varying light in accordance with the impulses in the output of said amplifier, and additional light control means connected in the plate supply lead of said amplifier for controlling light in accordance With the mean value of said impulses, whereby the light beam is controlled in accordance With both said impulses and the mean value of said impulses.

2. Sound recording apparatus including, a push-pull amplifier biased to cut-off, a transformer connected in the output of said amplier, a galvanometer connected in series With the secondary of said transformer, a light control shutter connected in series with the plate supply lead of said amplifier, means directing a light beam into cooperative relation with both said galvanometer and said shutter whereby the light beam is modulated in accordance with the audio output of the amplifier and the plate current supply to said amplifier.

3. Recording apparatus of the type described including an amplifier having a plate input current varying in accordance with the Volume of the plate output, means for supplying impulses to the input of said amplifier, means for supplying plate current to said amplifier, means for recording the amplified impulses, means connected in the plate supply circuit for filtering out audio impulses, and means also connected in the plate supply circuit and actuated by the filtered plate supply current for modifying the record of the amplified impulses in accordance with the envelope of the sound record.

MAX CARTER BATSEL. HERBERT BELAR. 

